digraph network {
    /* the links to the nodes */
    "S1" -> "H1" [ comment = "H1" ];
    "S1" -> "H2" [ comment = "H2" ];
    "S1" -> "H3" [ comment = "H3" ];
    "S1" -> "H4" [ comment = "H4" ];
    "S2" -> "H5" [ comment = "H5" ];
    "S2" -> "H6" [ comment = "H6" ];
    "S2" -> "H7" [ comment = "H7" ];
    "S2" -> "H8" [ comment = "H8" ];
    "S3" -> "H9" [ comment = "H9" ];
    "S3" -> "H10" [ comment = "H10" ];
    "S3" -> "H11" [ comment = "H11" ];
    "S3" -> "H12" [ comment = "H12" ];
    "S4" -> "H13" [ comment = "H13" ];
    "S4" -> "H14" [ comment = "H14" ];
    "S4" -> "H15" [ comment = "H15" ];
    "S4" -> "H16" [ comment = "H16" ];

    /* the links from the nodes */
    "H1"  -> "S1" [ comment = "*" ];
    "H2"  -> "S1" [ comment = "*" ];
    "H3"  -> "S1" [ comment = "*" ];
    "H4"  -> "S1" [ comment = "*" ];
    "H5"  -> "S2" [ comment = "*" ];
    "H6"  -> "S2" [ comment = "*" ];
    "H7"  -> "S2" [ comment = "*" ];
    "H8"  -> "S2" [ comment = "*" ];
    "H9"  -> "S3" [ comment = "*" ];
    "H10" -> "S3" [ comment = "*" ];
    "H11" -> "S3" [ comment = "*" ];
    "H12" -> "S3" [ comment = "*" ];
    "H13" -> "S4" [ comment = "*" ];
    "H14" -> "S4" [ comment = "*" ];
    "H15" -> "S4" [ comment = "*" ];
    "H16" -> "S4" [ comment = "*" ];

    /* the links up */
    "S1" -> "S11" [ comment = "H5,H9,H13" ];
    "S1" -> "S11" [ comment = "H6,H10,H14" ];
    "S1" -> "S12" [ comment = "H7,H11,H15" ];
    "S1" -> "S12" [ comment = "H8,H12,H16" ];
    "S2" -> "S11" [ comment = "H1,H9,H13" ];
    "S2" -> "S11" [ comment = "H2,H10,H14" ];
    "S2" -> "S12" [ comment = "H3,H11,H15" ];
    "S2" -> "S12" [ comment = "H4,H12,H16" ];
    "S3" -> "S11" [ comment = "H1,H5,H13" ];
    "S3" -> "S11" [ comment = "H2,H6,H14" ];
    "S3" -> "S12" [ comment = "H3,H7,H15" ];
    "S3" -> "S12" [ comment = "H4,H8,H16" ];
    "S4" -> "S11" [ comment = "H1,H5,H9" ];
    "S4" -> "S11" [ comment = "H2,H6,H10" ];
    "S4" -> "S12" [ comment = "H3,H7,H11" ];
    "S4" -> "S12" [ comment = "H4,H8,H12" ];

    /* the links down */
    "S11" -> "S1" [ comment = "H1,H2" ];
    "S11" -> "S1" [ comment = "H3,H4" ];
    "S11" -> "S2" [ comment = "H5,H6" ];
    "S11" -> "S2" [ comment = "H7,H8" ];
    "S11" -> "S3" [ comment = "H9,H10" ];
    "S11" -> "S3" [ comment = "H11,H12" ];
    "S11" -> "S4" [ comment = "H13,H14" ];
    "S11" -> "S4" [ comment = "H15,H16" ];
    "S12" -> "S1" [ comment = "H1,H2" ];
    "S12" -> "S1" [ comment = "H3,H4" ];
    "S12" -> "S2" [ comment = "H5,H6" ];
    "S12" -> "S2" [ comment = "H7,H8" ];
    "S12" -> "S3" [ comment = "H9,H10" ];
    "S12" -> "S3" [ comment = "H11,H12" ];
    "S12" -> "S4" [ comment = "H13,H14" ];
    "S12" -> "S4" [ comment = "H15,H16" ];
}
